Apparatus for measuring the state of compression of a liquid in a liquid vapor phasesystem



2,444,358 PRESSIONV ATTORNEYA June 29, 1948- A. A. MARKsoN ET AL APBRATUS FOR MEASURING THE STATE OF COM OF A LIQUID IN A LIQUID VAPOR PHASE SYSTEM` Filed Jah. 18,' 1944 Patented June 219, i943 UNITED STATES PATENT .OFFICE 2,444,358 PPAR'TUS FOR .MEASURING THE STATE 'OF CM'PRESSION 0F A LIQUID IN A LIQ- UI'D VAPOR PHASE SYSTEM -Alfred A. Markson, Mount Lebanon, and Robert Donaldson, Forest Hills, Pa., -assignors to John M. Hopwood, `Mount Lebanon, Pa.

Applicationilanuary 18, 1944, Serial No. "518;698

1 Claim. l

.This invention relates =to apparatus for mea-s- `ruring `the state ci compression of a liquid in a lliquidvaporpl'lasesystein.

In accordance with this invention we utilize in `its practice the principle that a pure liquid `in contact with its own vapordevelops .a vapor pressure which corresponds uniquely to its temperature so thatforevery vapor pressure the liq- :uid :will have :a denite temperature. This is also true oi' many mixtures and solutions. Under certain conditions the actual measuredtemperature of a liquid in a vesselirnay not correspond to this relationship of temperature vand `pressure `for two reasons. One is that the vapor phase Amay be contaminated `Icy another Vgas which exerts its own partial Apressure and second `the pressure may be measured at a point in the liquid where there is considerable hydrostatic head or pressure. The difference between the actual state of the pressure in the liquid and ithat :which corresponds to the unique temperature pressure curve of the liquid willbe referred toas the compression of :the 'liquid above its saturation pressure 'corresponding to its temperature, hereafter referred to as the compression of the liquid.

The presentl invention provides simple and accurate fmeans for measuring the difference between the actual pressure and the saturation pressure corresponding to the temperature of Vthe lqn Iuid, or theicompression of the liquid.

In `other words, if Px is the actual absolute pres- 1sure at anypoint in a liquid vapor system and Ps .is the saturation pressure which corresponds to `the temperature at the same point the instruvproblem isfencountered of preventing the feed waiter 'from flashing into steam at ythe suction of the boiler feed Lpumps, resulting from the vapor pressure in the heater decreasing to a `point where the state of compression of the liquid is reduced to the point `where the liquid would flash into steam or otherwise seriously increase pump cavitation.

An object of this invention is the provision of means for measuring the actual absolute pressure at any desired poin-t in a liquid vapor system and the saturation pressure of the liquid corresponding to its tempera-ture at the same point or other desired point and thereby determine the difference between such pressures.

The foregoing and other objects, as Well as other applications of the invention, Will be apparent from the following description taken in conjunction With the accompanying drawings, in which:

Fig. 1 is a diagrammatic view illustrating the temperature and pressure Vrelationship in a lliquid vapor system, lfor `example, a closed contact feed water heater, land yits application in the `practice of the invention;

Fig. 2 is a similar View illustrating how, -in accordance with the invention, a measurement .of

the difference between the absolute pressure ,of the liquid and the saturation pressure of the fliq; uid corresponding to the temperature of the liquid, may-be obtained;.and t Fig. 3 is a diagrammatic illustration -of .a pressure temperature-and saturation curve for a liquid vaporsystem. n

In the diagrammatic viewof Fig. 1, the numeral 1 designatesa container for a liquid the .level of which isfdesignated -by the numeral 2. Container l may be a closed :contact :boiler'feed -Water heater supplied with steam ffor heating watersupplied thereto .and an outlet through which the feed w-ater 'passes to the boiler feed pump (not shown).

`A :thermometer 3 extends into `the liquid whose temperature reading would give a true ymeasure lof `the pressure if there were no static head Vor `designate pressures at different Apoints in .con-

tainer l. rlhefpressure P1 in the space 3 above the level of the liquid includes the partial pressure of air :in the container `as `Well as the vapor pressure; 'the pressure P2 `is the same as PE1, `and the pressure P3 represents `the actu-alpressurecf the liquid :at anypoint x, and is a function ofthe .temperature of the liquid and the sum `of `the static head h2 and pressure `P1 represented also ashi. i

:InFig 2, the arrangement illustrated provides means for indicating the diierence between ,the `actual absolute 'pressure of the liquid'at any point,

`as at .pointxr, andthe saturation pressureeof the liquidfcorresponding `toits temperature; This dif ference may be 1expressed as CPI-P8), where Px is the total for -actual absolute pressure existing .at point .c and Ps is the saturation pressure of the liquid corresponding to its temeprature. In Fig. 2, a pointer 5 indicates the difference (Ps-Ps) by means to be described. Pointer 5 is fulcrumed at 5a and is mounted to sweep over a scale 6 calibrated suitably in terms of (Ps-PSL A spring 1 may `be utilized to bias the pointer in a desired manner.

The saturation pressure of the liquid corresponding to its temperature is developed by means of a container 8 disposed in the liquid of the container, pressure responsive element Ill and a connecting tube 9. Container 8, tube 9, and bellows I comprise a sealed system. .A liquid is introduced into container 8-this liquid being of the same kind as the liquid in'container I-and the system is exhausted of air so that the pressure developed by vaporization of the liquid Will represent the saturation pressure of the liquid at its temperature.

The pressure of the liquid Px in container I is measured by means of a pressure responsive element I2 and a tube II connected to the liquid at any desired point as at x. The pressure at :v includes the pressure h1 and h2 that is the sum ofv these pressures. Bellows Ill and I2 are connected together by a strut I3 which isturn is connected to pointer 5 so that as the strut is moved in response to the differential expansion or contractions of bellows I0 and I2, the pointer is posin tioned to indicate the difference (Pa-Ps).

1f the liquidin the Vapor pressure tube or container 8 isa pure liquid and if tube 9, conduit 9, and the pressure space about bellows I0 is exhausted of air and extraneous gases, and if the liquid in vcontainer 8 is the same as that in container I, the liquid in tube 8 will have a pure vapor phase; therefore, the pressure developed by vapor from the liquid in tube 8 will be its saturation pressure corresponding to the temperature of the liquid.

ySince the liquid in tube 8 is not exposed to the static pressure of the liquid in container I, the

'pressure on bellows Il) is a function of the ternperature of that liquid only. However, the pressure Ps of the vapor exerted on bellows I9 is actedupon differentially by the total pressure Px of the liquid in container I by communication of the liquid through conduit I I with the bellows I2 and the resulting displacement of the indicator 5 would be proportional to (PJWPS) and indicate the state of compression of the liquid at the point rc.

In Fig. 3, curve Px represents the total pressure temperature relation of the liquid existing at any Vpoint in a liquid vapor system, i. e. in a system where the vapor is in contact with its mother liquid', and curve Ps represents the saturated pressure of the liquid corresponding to its temperature.v Thus it will be seen that -if the total pressure Px is decreased from say point E, curve Px to F, curve Ps, that the temperature of the liquid must be cooled from temperature ter to tu in order to maintain the liquid in a state of compression at *which the liquid will not flash into vapor.

The pressure differential or compression of the liquid may be usefully applied to regulate the feed water supply to a boiler so as to prevent flashing of the feed water into steam or excessive Tcavitation, in feed water pumps. It is well known that the bleed pressure is high at high turbine loads and that if the load suddenly drops, high temperature and low static pressure results in feed water heaters causing feed Water to flash into steam at the suction of the boiler feed pumps and in the pumps also. By utilizing a device for measuring and controlling the compression of the liquid in the boiler feed line the compression of the liquid may be indicated and the condition corrected. This is also known as maintaining an effective submergence of the pumpsuction.

Having thus described the invention, what We desire to claim and secure by Letters Patent is:

Apparatus for measuring the state of compression of a liquid at any predetermined point in a liquid vapor system comprising a pressure actuated device having pressure receiving chambers provided with flexible means responsive to changes in the value of pressure in said chambers 'and adapted to deflect in response to the diff-erence between the pressures in said chambers,

,means operatively connected to said ilexible means for indicating the diiferential between the pressures acting thereon, a container, a tube connected to said container and one of said receiving chambers, the container having liquid therein whose saturation pressure at the temperature of the liquid in said system is substantially equal to that of the latter, said container, receiving chamber and tube connecting the same being substantially exhausted of air and sealed, said other receiving chamber being provided with means for connecting the same to the liquid vapor system so as to render the same responsive to the pressure of Athe liquid therein at said predeterminedpoint, whereby one of said receiving chambers is exposed to a vapor pressure corresponding to the vsaturation pressure of the liquid in the system at 'the temperature of said liquid, and the other of said chambers is subjected to thepressure of the liquid in said system at sai-d predetermined point.

The following references are of record in the le of this patent:

UNITED STATES PATENTS Number f Name Date 943,260 Lothrop et al Dec. 14,1909 1,248,698 Murray Dec. 4, 1917v 1,446,097 Lindbom et al Feb. 20, 1923 1,531,258 Kieser Mar. 24, 1925 1,545,938 Bren July 14, 1925 1,804,212 De Giers May 5, 1931 1,819,244 Jacobus Aug. 1S, 1931 1,917,810 Reynoldson July 11, 1933 2,068,663 Diehl Jan. 26, 1937 2,091,848 Eggers Aug. 31, 1937 2,152,979 Schwander Apr. 4, 1939 2,185,803 Diedrich J an. 2, 1940 2,200,471 Dickey May 14, 1949 2,268,469 Barnhart Dec. 30, 1941 2,335,250 Adlam Nov. 30, 1943 FOREIGN PATENTS Number Country Date 11,798 Great Britain May 12, 1910 

